Fuel injection valve for internal combustion engines

ABSTRACT

A fuel injection valve having a valve body, in which a bore with a pistonlike valve member disposed in it is embodied, which valve member is longitudinally displaceably in the bore counter to a closing force and by its longitudinal motion controls at least one injection opening, through which fuel can be injected into the combustion chamber of the engine. A valve holding body is braced axially against the valve body. An inlet conduit, which carries fuel at high pressure, extends through the valve holding body and its contact face, embodied as a high-pressure sealing face, on the valve body as far as the injection openings. The bracing of the valve holding body against the valve body is effected by means of a lock nut, which grips the valve body and with a female thread engages a male thread embodied on the valve holding body. The contact flank of the male thread and the contact flank of the female thread, which are pressed against one another by the bracing, are embodied substantially perpendicular to the longitudinal axis of the male thread, so that upon the bracing of the lock nut, no substantial radial forces oriented outward against the lock nut result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 00/00910 filed onAug. 4, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an improved fuel injection valve forinternal combustion engines, preferably internal combustion engines withself ignition.

2. Description of the Prior Art

In one known fuel injection valve, disclosed in German Utility Model 29814 934, a bore is embodied in a valve body, and in the bore a pistonlikevalve member is disposed longitudinally displaceably; by itslongitudinal motion, the valve member controls the opening of at leastone injection opening. The valve member is urged in the closingdirection by a closing force and has a pressure face, which is disposedin a pressure chamber that can be filled with high fuel pressure.Filling the pressure chamber with fuel at high pressure makes itpossible to exert a hydraulic force on the pressure face that isoriented counter to the closing force and thus brings about the openingstroke motion of the valve member. The device for generating the closingforce is embodied in a valve holding body, which has a longitudinal axisand is braced axially against the valve body. A high-pressure connectionis located on the valve holding body and discharges into an inletconduit that penetrates the valve holding body longitudinally andextends through the contact face between the valve body and the valveholding body as far as the inside of the pressure chamber of the valvebody. The contact face is accordingly a high-pressure sealing face andmust have a correspondingly good seal.

The bracing of the valve holding body against the valve body if effectedby a lock nut, which surrounds the valve body and contacts anannular-disklike contact face, embodied on the valve body, that facesaway from the valve holding body. On the valve holding body, there is amale thread engaged by the lock nut with a corresponding female thread,so that the valve body is braced against the valve holding body by thescrewing action of the lock nut. As a result, a good seal is achieved atthe high-pressure sealing face between the valve holding body and thevalve body, and the inlet conduit that passes through the high-pressuresealing face, that is, the contact face of the valve holding body at thevalve body, is securely sealed off.

In the known fuel injection valves, the thread, embodied on the outerjacket face of the valve holding body and engaged by the lock nut, isembodied as a fine thread. The flanks of the thread courses form anangle of about 60° with the longitudinal axis of the thread and thusalso with the longitudinal axis of the valve holding body. Thus becauseof the axial bracing of the lock nut, along with the axially operativeforce component on the screw faces, a force component acting in theradial direction to the longitudinal axis of the valve holding body isalso obtained, which expands the lock nut. This limits the maximumattainable pressure per unit of surface area at the high-pressuresealing face between the valve holding body and the valve body, so thatat high pressures in the inlet conduit, sealing problems can occur.

SUMMARY OF THE INVENTION

The fuel injection valve of the invention has the advantage over theprior art that the contact flanks of the male thread embodied on thevalve holding body and of the female thread embodied on the lock nut areat least approximately perpendicular to the longitudinal axis of thevalve holding body, so that upon the bracing of the lock nut, thesecontact flanks are pressed against one another without substantialradial forces on the lock nut being engendered. As a result, greateraxial clamping forces can be exerted on the valve body and the valveholding body, and a higher pressure per unit of surface area can thus beachieved at the high-pressure sealing face between the two bodies.Expansion of the lock nut from radial force components thus no longeroccurs. This is especially advantageous in fuel injection valves thatwork with a so-called common rail system, because in that case aconstantly high fuel pressure prevails in the valve body.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent fromthe detailed description contained below, taken with the drawings, inwhich:

FIG. 1 is a longitudinal section through a fuel injection valve of theinvention;

FIG. 2 shows an enlarged detail of FIG. 1 in the region of the malethread of the valve holding body; and

FIG. 3 shows a further exemplary embodiment of a fuel injection valve ofthe invention in longitudinal section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a fuel injection valve of the invention in longitudinalsection. A valve holding body 1 is braced axially against a valve body3. The valve body 3 is embodied with a graduated diameter and taperstoward the combustion chamber, so that an annular-disklike contact face24 oriented toward the combustion chamber is formed on its outer jacketface. A lock nut 5 grips the valve body 3 and rests on the contact face24, extending to beyond the valve body 3. On the inner jacket face ofthe lock nut 5, at the level of the valve holding body 1, a femalethread 44 is formed, which engages a male thread 42 embodied on theouter jacket face of the valve holding body 1; this male thread 42 has alongitudinal axis 8. Hence turning the lock nut 5 moves the lock nut 5in the axial direction and thus braces the valve body 3, with its endface remote from the combustion chamber, against the valve holding body1, so that the contact face of the valve body 3 at the valve holdingbody 1 is embodied as a high-pressure sealing face 30.

Embodied in the valve body 3 is a bore 7, which originates on the faceend of the valve body 3 remote from the combustion chamber and changesover, on its end toward the combustion chamber, into a valve seat 20.The valve seat 20 is embodied substantially conically and has at leastone injection opening 22, by way of which the bore 7 communicates withthe combustion chamber of the engine. A pistonlike valve member 10 isdisposed in the bore 7 and is guided sealingly in the bore 7 in aportion remote from the combustion chamber, while toward the combustionchamber it tapers, forming a pressure shoulder 16. On its end toward thecombustion chamber, the valve member 10 changes over into a valvesealing face 18, which is embodied substantially conically andcooperates with the valve seat 20 to control the at least one injectionopening 22. In the valve body 3, at the level of the pressure shoulder16, a pressure chamber 14 is embodied by a radial enlargement of thebore 7; the pressure chamber continues in the form of an annularconduit, surrounding the valve member 10, as far as the valve seat 20.An inlet conduit 12 embodied in the valve body 3 and in the valveholding body 1 discharges into the pressure chamber 14 and communicatesby its other end with a source of high fuel pressure, not shown in thedrawing. Via this inlet conduit 12, the pressure chamber 14 can befilled with fuel at high pressure.

In the valve holding body 1, there is a spring chamber 32 embodied as abore, in which a guide piece 40 is disposed that is connected to the endface, remote from the combustion chamber, of the valve member 10. Theguide piece 40 is embodied cylindrically here and is guided in thespring chamber 32. The guide piece 40 has at least one lateral recess41, which connects the bore 7 to the spring chamber 32. A closing spring34 embodied as a helical compression spring is disposed with pressureprestressing between the guide piece 40 and the end face, remote fromthe combustion chamber, of the spring chamber 32. This closing spring 34surrounds a tappet 36, which is disposed in a guide bore 38 thatdischarges into the spring chamber 32, and with its face end toward thevalve member 10, this tappet rests on the guide piece 40. By means of adevice not shown in the drawing, a controllable closing force acts onthe face end of the tappet 36 remote from the combustion chamber; thisforce is capable of urging the tappet 36 in the direction of the valveseat 20. In the closed state of the fuel injection valve, that is, whenthe valve sealing face 18 is resting on the valve seat 20, apredetermined high fuel pressure prevails in the pressure chamber 14because of the communication with the high-pressure fuel source. As aresult of this high fuel pressure, a hydraulic force on the pressureshoulder 16 is produced, resulting in an opening force acting on thepressure shoulder 16 in the direction away from the valve seat 20. Theclosing force on the tappet 36, which also acts on the valve member 10via the guide piece 40, predominates over this opening force, however,so that the valve member 10 remains in the closing position. The closingspring 34 still has a reinforcing effect at this time. If an injectionof fuel is to take place, then the closing force on the tappet 36 isreduced, and the hydraulic force on the pressure shoulder 16 is nowcapable of moving the valve member 10 in the opening direction, that is,away from the valve seat 20, counter to the closing force on the tappet36 and to the spring force of the closing spring 34. As a result, thevalve sealing face 18 lifts from the valve seat 20, the injectionopenings 22 are uncovered, and fuel flows out of the pressure chamber 14through the injection openings 22 into the combustion chamber of theengine. Via the inlet conduit 12, fuel at high pressure is constantlyresupplied from the high-pressure fuel source. The end of the injectionis brought about in turn by increasing the closing force on the tappet36, so that the valve member 10, as a result of the force ratiosdescribed above, returns to its closing position.

In FIG. 2, an enlargement in the region of the overlap of the lock nut 5and the valve holding body 1 is shown. The male thread 42 on the valveholding body 1 has an oblique flank 46 in every thread course; thisflank forms an angle β with the longitudinal axis 8 of the male thread42. The contact flank 52 facing the oblique flank 46 conversely forms anangle α with the longitudinal axis 8 of the male thread 42, and thisangle is preferably within the range about 85° to 95°, and morepreferably approximately 90°. The female thread 44 of the lock nut 5 isembodied so that it engages the male thread 42 of the valve holding body1. Each thread course of the female thread 44 has one oblique flank 48,which once the lock nut 5 has been screwed in faces the oblique flank 46of the male thread 42. The two oblique flanks 46, 48 are not generallypressed together, however, since the lock nut 5 is axially bracedagainst the valve holding body 1. The flank of the female thread 44facing the oblique flank 48 is embodied as a contact flank 50 and ispreferably within the range of about 85° to 95°, and more preferablyapproximately perpendicular to the longitudinal axis 8 of the valveholding body 1 and corresponding to the angle α of flank 52. The contactflank 50 rests on the contact flank 52 of the male thread 42, so thatwhen the lock nut 5 is screwed in tightly, an axially acting force istransmitted from the lock nut 5 via the outer contact flank 50 onto thecontact flank 52 of the male thread 42 of the valve holding body 1.Since the two contact flanks 50, 52 contacting one another areapproximately perpendicular to the longitudinal axis 8 of the malethread 42 and thus also approximately perpendicular to the bracingdirection of the valve body 3, there is no, or only a slight, resultantforce component in the radial direction relative to the longitudinalaxis 8 upon the lock nut 5. Accordingly no expansion of the lock nut 5from the tightening occurs, and hence at the high-pressure sealing face30, or in other words the contact face of the valve body 3 at the valveholding body 1, a very high pressure per unit of surface area can beachieved and accordingly an adequately good seal of the inlet conduit 12at its transition from the valve holding body 1 to the valve body 3.

In FIG. 3, as an alternative to the design shown in FIG. 1, a fuelinjection valve is shown in longitudinal section in which there is ashim 6 between the valve holding body 1 and the valve body 3, thuscreating two high-pressure sealing faces: first, at the transition fromthe valve holding body 1 to the shim 6, and second, from the shim 6 tothe valve body 3. In this kind of design as well, because of the threadaccording to the invention on the inside of the lock nut and on theouter jacket face of the valve holding body 1, an optimized pressure perunit of surface area is obtained, and thus improved tightness of theinlet conduit 12 at its transition from the valve holding body 1 to thevalve body 3 because of the high-pressure sealing faces.

Alternatively to the fuel injection valves shown in FIGS. 1 and 3, itcan also be provided that the lock nut with its female thread engages amale thread disposed on the outer jacket face of the valve body 3. Inthat case, the lock nut is braced on a contact face, embodied on thevalve holding body 1 facing away from the valve body 3, that in thiscase as well, a bracing of the valve body 3 and valve holding body 1against one another can be effected.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

I claim:
 1. A fuel injection valve for internal combustion engines,having a valve body (3) in which, in a bore (7), a valve member (10) islongitudinally displaceable counter to a closing force by subjection ofa pressure shoulder (16) to pressure by fuel, and by means of thelongitudinal motion controls at least one injection opening (22), andhaving a valve holding body (1), which is braced in the axial directionby means of a lock nut (5) against the valve body (3), wherein the locknut (5) has a female thread (44) which engages a male thread (42) thatis embodied on an outer jacket face of the valve holding body (1) or anouter jacket face of the valve body (3) and has a longitudinal axis (8),and having an inlet conduit (12) extending in the valve holding body (1)and in the valve body (3), through which conduit, fuel can be carried athigh pressure to the at least one injection opening (22) by means of acontact face, embodied as a high-pressure sealing face (30) of the valvebody (3) on the valve holding body (1), the improvement wherein contactflanks (50; 52) of the female thread (44) and the male thread (42),respectively, are pressed against one another to effect bracing of thevalve body (3) against the valve holding body (1), the contact flanks(50; 52) being embodied at least approximately perpendicular to thelongitudinal axis (8) which is surrounded by the male thread (42) andthe female thread (44).
 2. The fuel injection valve of claim 1, whereina shim (6) is disposed between the valve body (3) and the valve holdingbody (1).
 3. The fuel injection valve of claim 1, wherein the contactflank (50) of the female thread (44) and the contact flank (52) of themale thread (42) form an angle within the range of about 85° to 95° withthe longitudinal axis (8).